This invention relates in general to rock bits used for earth boring, and in particular to improvements in the bearing lubrication and the sealing system for such bits.
The drilling of holes in the mining industry is accomplished with either a liquid or an air circulating medium. The liquid of air is utilized principally to cool the bit and flush earth cuttings from the bottom of the borehole to the surface ot the earth.
Rock bits used with a liquid drilling medium (called here "mud bits") commonly have a seal between each rotatable cutter and its supporting bearing shaft. A lubrication system provides lubricant in the bearing spaces and a flexible diaphram compensator system adjusts the pressure of the lubricant to the general level of the liquid or drilling mud on the exterior of the bit. The hydrostatic pressure of this exterior mud increases with depth and the flexible diaphram correspondingly causes increases in the pressure of the liquid in the lubrication system.
There are special problems encountered when air or gas is utilized as the circulating medium and attempts are made to seal the bearing of a mining bit. It is common to see abrasive wear of the seal, apparently caused by abrasive material such as sand around the bearing seal, promoting its early failure. In the shallow holes of mining applications there is little or no positive lubricant pressure maintained in the bearings. Moderately high rotational speeds and heavy weights are used. As a result of these and other reasons, bits used with air and gas drilling (called here "air bits") typically have roller bearings and ball bearings, with passage means from the interior of the bit to permit a portion of the air or gas to flow through the bearings. This has the effect of cooling the bearings and reducing the heat buildup in the bearing areas. Air bits do not utilize a seal since a seal between a cutter and shaft would impede the flow of cooling air through the bearing.
In recent years there have been apparent attempts to utilize seals in air bits. In U.S. Pat. No. 4,102,419, which issued to Frank J. Klima on July 25, 1978, there is shown a bit with a sealing ring in a bearing composed of antifriction elements, with passage means to introduce cooling air into the bearing. One passage introduces air to a spring loaded sealing ring to flush cuttings or other debris away from the seal.
In U.S. Pat. No. 4,183,417, which issued to Bert G. Levefelt on Jan. 15, 1980, there is shown a rock bit used in air drilling with a seal ring and a jet slot for the discharge of air between an annular surface of the leg and a seal ring.
In U.S. Pat. No. 4,172,502, which issued to Hans B. van Nederveen on Oct. 30, 1979, there is shown a rock bit with a locking ring having a seat for mounting a resilient sealing member with an annular slit connected to a channel in the bit to direct the flow of drilling mud radially out within the slit to prevent the penetration of drilling debris around the seal.